The present invention relates to an apparatus for measuring the filling level of silos and other containers.
More particularly, the invention relates to an apparatus of the type mentioned above, which is especially suitable for continuous or discontinuous measuring of the filling level of silos and analogous containers for heavy goods, for example minerals used in the making of bituminous for road-construction purposes.
Apparatus of the general type here in question is already known. For instance, U.S. Pat. No. 4,043,199 discloses such an apparatus which has a vertically oriented electromagnetically actuated device for raising and lowering a measuring chain which depends from it into the interior of a container. The measuring chain passes through a cut-out spring and extends down to the bottom wall of the container. It is protected by a stationarily mounted hose which surrounds it. At the level of the spring the measuring chain carries a coupling device which, when actuated and when the lifting device is operated, permits a user to load the spring with the weight of that portion of the measuring chain which is hanging freely, i.e. which is not immersed in the contents of the container. In this manner the spring can be subjected to different spring tensions which constitute a measure for the level to which the container is filled with material. The spring, which bends under the influence of the chain weight extends transversely to the vertical elongation of the chain and, due to the electromagnetic construction of the lifting device, the latter also extends essentially transversely to the elongation of the chain, so that all in all this prior-art arrangement is relatively wide in its structural dimensions.
Another device for the purposes described above is disclosed in German Petty Patent GM 7,807,121. In this reference a frame is provided in the upper region of a silo and a measuring bridge is suspended from this frame via two springs. Parallel to this measuring bridge a lifting cylinder is connected to the frame and the measuring chain is movably and removably secured to the lifting cylinder. Parallel to the spring elongation and contraction path, there is provided a measuring device. A coupling arrangement is provided between the measuring chain and the measuring bridge so that in response to actuation of the lifting cylinder the weight of the free-hanging measuring chain can be disengaged from the lifting cylinder and shifted to the measuring bridge, with the result that the measuring device performs movement under the influence of this weight which indicate the filling level in the silo. Here, also, the lifting cylinder and the measuring bridge are connected in parallel with one another so that the device must necessarily be relatively wide in its structural dimensions.
In addition to the problems mentioned above, the prior-art devices of this type have the further disadvantage that the springs of the respective measuring bridge must always be fully loaded and subsequently fully unloaded, i.e. the spring or springs will always be stretched respectively moved through a rather large spring path in dependence upon the measured filling level in the silo. Moreover, there are applications in which a rather wide structural dimension of such a device is disadvantageous, because the region at the upper end or at the cover of the silo or container is often almost completely needed for the supply of the material into the container.